1. Field of the Invention
The present invention relates to an artificial saliva composition suitable for application to hydrodipsia (or thirst) caused by sialadenitis. More specifically, it relates to an artificial saliva composition having a pH buffering capability similar to natural saliva and a high caries preventing effect.
2. Description of the Related Art
Known in the art as an artificial saliva composition for application to, for example, hydrodipsia caused by sialadenitis, are aqueous solutions containing inorganic cations and anions contained in natural saliva, phosphate buffers for pH adjustment, and a thickening agent such as carboxymethyl cellulose. Various attempts have been made to improve the conventional artificial saliva compositions. For example, Japanese Unexamined Patent Publication (i.e., Kokai) No. 52-108014 (or JP-A-52-108014) proposes artificial saliva compositions further containing digestive enzymes, hormones, and bactericides in the above-mentioned conventional artificial saliva compositions. Japanese Kokai Nos. 59-7116 and 59-27818 propose artificial saliva compositions having a very low viscosity change over a wide pH range and containing, as a thickening agent, hydroxypropyl cellulose, methyl cellulose, or hydroxypropylmethyl cellulose.
Artificial saliva compositions are used as substituents for natural saliva and, therefore, should preferably possess all the functions of natural saliva. Of these functions of natural saliva, the pH buffering capacity is the most important, since the generation of caries can be inhibited by this pH buffering capacity. That is, caries occurs because enamels (i.e., hydroxyapatite) that form the surface layer of teeth, are subjected to decalcification by acids produced by microorganisms such as Streptococcus mutans. This decalcification is accelerated when the pH in the oral cavity becomes less than 5.5. Accordingly, to prevent the generation of caries, preferably the pH in the oral cavity is within the range of 5.5 or more. Natural saliva has a special buffering action, and the pH in the oral cavity is always maintained at a pH of 5.5 or more, whereby the generation of caries is inhibited.
However, the conventional artificial saliva compositions all have low pH buffering capacities and do not possess the special buffering actions of natural saliva.
Therefore, when conventional artificial saliva compositions are used, the pH in the oral cavity is greatly changed, and in particular, is decreased to a pH of less than 5.5 due to the presence of acids produced by microorganisms. As a result, the surface enamel of the teeth may be subjected to decalcification and caries may be generated.